1. Field of the Invention
The present invention relates to an information recording carrier for use in system for recording and/or reproducing information by optical means.
2. Description of the Related Art
Conventionally, a system for reading out information by moving the information recording carrier relatively has been available and optical means, magnetic means and electrostatic capacity means are used for reproducing information therefrom. Of them, the system for recording and/or reproducing information by the optical means has prevailed widely in daily life (“recording/reproducing” mentioned here means three statuses, namely, only recording, only reproduction or recording and reproduction).
For example, as a recording/reproducing type information recording carrier using beam having wavelength λ=650 nm, DVD-RAM, DVD-RW (“DVD” means digital versatile disc) and the like are available.
Although the recording/reproducing type information recording carriers have been developed as actual products and marketed, the technology for burying address information into such recording/reproducing type information recording carrier effectively has been still being developed and a next generation information recording carrier will need improvement of the conventional address recording technology or a new address recording technology.
The first purpose for burying address information effectively is to bury address information at a low error rate without substantially decreasing an area provided for recording/reproducing, and the second purpose is to bury the address information by suppressing the error rate of recording mark so that buried address information never interferes with a main recording/reproducing region.
As for the first object, for example, in the information-recording carrier employing a header type address represented by DVD-RAM (DVD rewritable), the address information is recorded by pit row (called header) by cutting a main recording/reproducing region. Because the header has the same format as the reproduction dedicated information-recording carrier, the error rate of the address information is suppressed very low.
However, because recording cannot be achieved in this header region, the entire capacity of an information-recording carrier whose area is limited drops. Thus, address recording system not using the header is necessary.
As for the second object, in the information recording carrier employing land pre-pit type address represented by for example, DVD-RW (DVD rerecordable), the recording/reproducing region is continuous and has no cut area. Although the address information is prepared as pits, that pits (land pre-pits) are dispersed widely so that they are recorded between a recording track and another recording track.
Thus, although the recording capacity does not drop, the land pre-pit and the recording signal (recording mark) interfere with each other because they are disposed in parallel. Consequently, the error rate of address rises so that the error rate of the recording mark may rise in some cases. Thus, an address recording system using no land pre-pit is necessary.
To solve such a request, there is a method for recording the address information by forming a groove substantially parallel to the information recording carrier continuously such that it is wobbled.
For example, for the rewritable DVD disc (so-called DVD+RW) described in ECMA/TC31/99/43, an address recording method of wobbling the groove by phase shift modulation is determined. Because according to this recording method, an address is recorded in the groove by phase shift modulation, the header is not necessary and the capacity is not lost.
FIG. 1 shows the concept of the phase shift modulation in this rewritable DVD disc.
As the minute pattern, plural substantially parallel groove continuities 150 are formed. Each of the continuities 150 is comprised of a groove 151 and an inter-groove portion 152 such that both are formed substantially parallel to each other.
In the meantime, the groove 151 and the inter-groove portion 152 have different heights (a difference in height is for example, λ/8 n when the recording wavelength is λ and the refractivity of a recording light transmitting member is n). Then, the groove 151 is wobbled in the shape of sine wave.
The address is recorded such that phase information is given to this groove 151 as shown in FIG. 2. That is, sin 0 and sin π are handled as 0 and 1 when the address information is recorded. Because upon reproduction, a phase switching point 153 is loaded with the address information, it can be reproduced by for example, envelop phase detection of the push-pull signal.
If the address information is recorded by phase shift modulation like this, the header is not necessary and the capacity is not lost. Further, reproduction is enabled by well known envelope phase detection.
When the inventor of the present invention considered this address recording method under various unfavorable conditions, more specifically, recorded user data into the groove 151 in a disc of phase change type created based on this method and tried to reproduce the address, it was found that the recorded user data leaked into the address signal thereby causing a trouble in address detection.
The frequencies for the recording data and address information never overlap because their information densities are different. However, in viewpoint of address reproduction, recording user data acted like noise and it was found that detection of the address, more specifically detection of the phase switching point 153 was often mistaken. Although when the reproduction by envelope phase detection was replaced with the reproduction by synchronous phase detection as its countermeasure, the error rate dropped by about 1 digit, the effect was not sufficient.
Further, wobbling of the sine wave was increased so as to reduce the error rate. In this case, although there was some extent of the effect, interference increased so that the error rate of user recording worsened or in worst case, the tracking became unstable.
This problem is originated from a fact that this address recording method depends on minute change in shape of the phase switching point 153.
Further, under this address recording method, address in adjacent tracks leaked so that it was mixed into main address about once every several tracks. As a result, not only the phase switching point 153 is difficult to detect, but also this phenomenon reduces the reliability of the information recording carrier remarkably.
Thus, a novel recording method by other modulation than the phase shift modulation and based on the groove continuity structure by making advantage of data recording by wobbled groove has been demanded.
Therefore, the present invention proposes a groove modulation method, which can replace the phase shift modulation so as to bury the address information effectively.
More specifically, the first object is to bury address at a low error rate without reducing the area provided for recording/reproduction, the second object is to bury the address by suppressing the error rate of a recording mark so that it does not interfere with the main recording/reproduction region. The third object is to construct so that the buried address does not interfere with adjacent addresses.
In the meantime, the present invention considers that gallium nitride base compound semiconductor light emission device (for example, described in Japanese Patent No. 2778405) recently developed to raise the recording density of the information recording carrier, that is, short-wave laser which emits light in the vicinity of λ=350 to 450 nm produces more noise than a conventional laser.
Further, although technology for forming the information recording carrier in multiple layers so as to increase its recording capacity has been well known, it must be considered that noise in the reproducing system is increased by this multiple-layers.
Further, the present invention aims at corresponding to a recently developed light transmission layer incident information recording carrier from viewpoints of physical structure.